Soft magnetic material powder and manufacturing method thereof, and magnetic core and manufacturing method thereof

ABSTRACT

A soft magnetic material powder includes soft magnetic material particles, the soft magnetic material particles each include a core formed from an Fe-based soft magnetic material and an insulating film covering the surface of the core, and the insulating film contains an inorganic oxide and a water soluble polymer. A magnetic core includes soft magnetic material particles and a binder bonding the soft magnetic material particles to each other, the soft magnetic material particles each include a core containing an Fe-based soft magnetic material and an insulating film covering the surface of the core, and the insulating film contains an inorganic oxide and a water soluble polymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to Japanese PatentApplication 2014-209308 filed Oct. 10, 2014, and to International PatentApplication No. PCT/JP2015/075945 filed Sep. 14, 2015, the entirecontent of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a soft magnetic material powder usedfor a magnetic core and a manufacturing method thereof. In addition, thepresent disclosure also relates to a magnetic core using this softmagnetic material powder and a manufacturing method of the magneticcore.

BACKGROUND

In recent years, in concomitance with the reduction in size of electricapparatuses and electronic apparatuses, magnetic cores formingtransformers and coils, which are used for the above apparatuses, arerequired to have characteristics, such as a high magnetic permeabilityand a low eddy-current loss, at a high frequency. Accordingly, in orderto obtain a low eddy-current loss in a high frequency band, the magneticcore is required to have a high electric resistance. As one example ofthe magnetic core as described above, for example, there has been apowder magnetic core formed in such a way that after a magnetic materialis formed into a fine particulate powder, the surface of each particleis covered with an insulating film, and the particles thus treated areprocessed by compression molding. Compared to the case in which a bulkymagnetic material is used, by the powder magnetic core, although themagnetic permeability is decreased, in particular, the electricresistance can be significantly increased, and the eddy-current loss canbe remarkably decreased.

Heretofore, a method has been known in which after hydroxides areadsorbed on the surface of pure Fe which is a magnetic material powderby hydrolysis of a metal alkoxide, a sintered body is obtained bypressing the powder thus obtained (for example, see Japanese UnexaminedPatent Application Publication No. 09-125111).

In addition, a manufacturing method to obtain a molded powder compacthas been known (for example, see Japanese Unexamined Patent ApplicationPublication No. 2012-172172). In this method, after a compaction moldingpowder in which a metal alkoxide and a mineral containing crystal waterare present on surfaces of soft magnetic metal particles and thiscompaction molding powder are compressed to form a green molded body,this green molded body is annealed to hydrolyze the metal alkoxide andto generate insulating films on the surfaces of the soft magnetic metalparticles.

SUMMARY Technical Problem

The magnetic material powder disclosed in Japanese Unexamined PatentApplication Publication No. 09-125111 has a good insulating property,and a thin inorganic film is formed on the surface of the metal magneticpowder. On the other hand, the fluidity in powder compaction molding isinferior, and the magnetic permeability of the powder magnetic core isnot increased, and furthermore, there have been problems in that finecracks are generated in the organic films in powder compaction molding,the electric resistance is decreased in annealing, and the eddy-currentloss is increased.

Since the molded powder compact disclosed in Japanese Unexamined PatentApplication Publication No. 2012-172172 has a high film strength of theinsulating film, no cracks are generated in powder compaction molding,and the electric resistance is not decreased in annealing. However,there have been problems in that since the mineral is added, a thin filmcannot be formed, the density of a magnetic powder of the powdermagnetic core is not increased, and as a result, the magneticpermeability is not sufficiently increased.

The present disclosure aims to provide a soft magnetic material powdercapable of obtaining a magnetic core having a sufficient density, a highmagnetic permeability, and also a high electric resistance.

Solution to Problem

A soft magnetic material powder according to the present disclosurecomprises:

soft magnetic material particles,

wherein the soft magnetic material particles each include:

a core formed from an Fe-based soft magnetic material; and

an insulating film covering the surface of the core, and

the insulating film contains an inorganic oxide and a water solublepolymer.

Advantageous Effects of Disclosure

According to the soft magnetic material powder of the presentdisclosure, when a magnetic core is molded therefrom, as the softmagnetic material, a sufficient density can be obtained, and themagnetic permeability of the magnetic core can be increased. Inaddition, by the insulating film and a binder of each soft magneticmaterial particle contained in the soft magnetic material powder, amagnetic core having a high electric resistance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross-sectional view showing a finecross-sectional structure of a soft magnetic material particle containedin a soft magnetic material powder according to Embodiment 1.

FIG. 2 is an enlarged cross-sectional view showing a finecross-sectional structure of a magnetic core according to Embodiment 1.

FIG. 3 is a schematic view showing analytical positions at each of whicha composition analysis is performed, the analytical positions beinglocated on the line extending from a core to an insulating film and abinder of a soft magnetic material particle which forms thecross-sectional structure of the magnetic core shown in FIG. 2.

FIG. 4 is a graph showing composition analysis results obtained alongthe line shown in FIG. 3.

FIG. 5 is a graph showing the relationship between an applied voltageand a specific resistance measured by a high resistance measurementdevice.

DETAILED DESCRIPTION

A soft magnetic material powder according to a first aspect comprises:

soft magnetic material particles,

wherein the soft magnetic material particles each include:

a core formed from an Fe-based soft magnetic material; and

an insulating film covering the surface of the core, and

the insulating film contains an inorganic oxide and a water solublepolymer.

In a soft magnetic material powder according to a second aspect, thewater soluble polymer described in the above first aspect may be atleast one selected from the group consisting of a poly(vinylpyrrolidone), a poly(ethylene imine), a carboxymethyl cellulose, agelatin, a poly(acrylic acid), a poly (ethylene glycol), and a poly(vinyl alcohol).

In a soft magnetic material powder according to a third aspect, thewater soluble polymer described in the above first aspect is apoly(vinyl pyrrolidone) and may be contained in a range of 0.01 to 1percent by weight.

In a soft magnetic material powder according to a fourth aspect,

wherein the inorganic oxide described in any one of the above first tothird aspects may be at least one selected from the group consisting ofTiO₂, SiO₂, Al₂O₃, and ZrO. The inorganic oxide may also be apolysiloxane.

In a soft magnetic material powder according to a fifth aspect, theinorganic oxide described in any one of the above first to third aspectsis SiO₂ and may be contained in a range of 0.01 to 5 percent by weight.

In a soft magnetic material powder according to a sixth aspect, theFe-based soft magnetic material described in any one of the above firstto fifth aspects may be at least one selected from the group consistingof Fe, FeNi, FeCo, FeSi, FeSiCr, FeSiAl, and FeSiBCr.

A method for manufacturing a soft magnetic material powder according toa seventh aspect comprises:

dispersing an Fe-based soft magnetic material in a solvent; and

adding a metal alkoxide and a water soluble polymer to the solvent tohydrolyze the metal alkoxide and to form insulating films eachcontaining a metal oxide, which is a hydrolysate of the metal alkoxide,and the water soluble polymer on surfaces of soft magnetic materialparticles which form the Fe-based soft magnetic material powder, so thatan insulating treatment is performed on the soft magnetic materialparticles.

A magnetic core according to an eighth aspect comprises the softmagnetic material powder according to any one of the above first tosixth aspects.

A magnetic core according to a ninth aspect is a magnetic core whichcomprises:

soft magnetic material particles; and

a binder which bonds the soft magnetic material particles to each other,

wherein the soft magnetic material particles each include:

a core containing an Fe-based soft magnetic material; and

an insulating film covering the surface of the core, and

the insulating film contains an inorganic oxide and a water solublepolymer.

A magnetic core according to a tenth aspect is a magnetic core whichcomprises:

soft magnetic material particles; and

a binder which bonds the soft magnetic material particles to each other,

wherein the soft magnetic material particles each include:

a core formed from an Fe-based soft magnetic material; and

a Si-containing insulating film covering the surface of the core,

the Fe-based soft magnetic material includes Fe and Cr, and

the insulating film contains an inorganic oxide in which the amount ofSi is larger than that of Cr.

A method for manufacturing a magnetic core according to an eleventhaspect comprises:

mixing the soft magnetic material powder according to any one of theabove first to sixth aspects and a thermosetting resin functioning as abinder to form a mixture; and

heat-curing the mixture to obtain a magnetic core.

A method for manufacturing a magnetic core according to a twelfth aspectcomprises:

mixing the soft magnetic material powder according to any one of theabove first to sixth aspects and a thermosetting resin functioning as abinder to form a mixture; and

after the thermosetting resin is cured by heating the mixture,performing an annealing treatment to obtain a magnetic core.

An electronic component according to a thirteenth aspect comprises themagnetic core according to any one of the above eighth to the tenthaspects.

Hereinafter, a soft magnetic material powder and a manufacturing methodthereof and a magnetic core and a manufacturing method thereof accordingto embodiments will be described with reference to the attacheddrawings. In addition, in the drawings, substantially the same membersare designated by the same reference numeral.

Embodiment 1 Soft Magnetic Material Powder

FIG. 1 is a cross-sectional view showing a cross-sectional structure ofa soft magnetic material particle 10 included in a soft magneticmaterial powder according to Embodiment 1. This soft magnetic materialparticle 10 has a core containing an Fe-based soft magnetic material andan insulating film 2 covering the surface of the core 1. The insulatingfilm 2 contains an inorganic oxide and a water soluble polymer.

In this soft magnetic material powder, since a raw material of theinsulating film 2 contains a water soluble polymer together with aninorganic oxide, a thin insulating film 2 can be obtained. Furthermore,since a flexible water soluble polymer is present in the insulating film2, a stress generated in compression molding can be reduced, and hence,molding can be performed at a low pressure. As a result, even incompression molding for manufacturing of a magnetic core, no cracks aregenerated in the insulating film 2 of the soft magnetic materialparticle included in the soft magnetic material powder. That is,according to this soft magnetic material powder, excellent compressionmoldability can be obtained.

The average particle diameter of the core 1 containing the Fe-based softmagnetic material of the soft magnetic material particle 10, which formsthis soft magnetic material powder, is, for example, in a range of 0.1to 100 μm. The thickness of the insulating film 2 of the soft magneticmaterial particle 10 is, for example, in a range of 5 to 100 nm andpreferably in a range of 20 to 40 nm. The thickness was measured by atransmission electron microscope (TEM). In particular, by the use of athin sample obtained by processing a magnetic core, the thickness of theinsulating film 2 was measured at 5 locations of each of 5 viewingfields of the observation image by a transmission electron microscope ata magnification of 100,000 to 200,000 times, and the average valueobtained therefrom was regarded as the thickness of the insulating film2.

Hereinafter, members forming this soft magnetic material powder will bedescribed.

Fe-Based Soft Magnetic Material: Core

As the Fe-based soft magnetic material used for the core 1, for example,Fe and an alloy containing Fe may be used. As the alloy containing Fe,for example, various Fe-based magnetic metals, such as FeNi, FeCo, FeSi,FeSiCr, FeSiAl, and FeSiBCr, which have been used in the past, may bementioned. The soft magnetic material may further contain an impurity.

Insulating Film

The insulating film 2 contains an inorganic oxide and a water solublepolymer.

Inorganic Oxide

As a metal element M forming the inorganic oxide, at least one typeselected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Ti, Cu,Sr, Y, Zr, Ba, Ce, Ta, and Bi may be used. In addition, for example, inconsideration of the strength and the inherent specific resistance of anoxide to be obtained, Si, Ti, Al, and Zr are preferable. This metalelement M is a metal of a metal alkoxide used to form the insulatingfilm 2. As a concrete inorganic oxide, SiO₂, TiO₂, Al₂O₃, or ZrO ispreferable. SiO₂ is particularly preferable.

In addition, the inorganic oxide is contained in a range of 0.01 to 5percent by weight with respect to the soft magnetic material powder.

Water Soluble Polymer

As the water soluble polymer, at least one selected from the groupconsisting of a poly(ethylene imine), a poly(vinyl pyrrolidone), apoly(ethylene glycol), a sodium polyacrylate, a carboxymethyl cellulose,a poly(vinyl alcohol), and a gelatin may be used, or at least two typesthereof may be used in combination.

The water soluble polymer is contained in a range of 0.01 to 1 percentby weight with respect to the soft magnetic material powder.

Method for Manufacturing Soft Magnetic Material Powder

A method for manufacturing this soft magnetic material powder will bedescribed.

-   (1) An Fe-based soft magnetic material powder is dispersed in a    solvent.-   (2) A metal alkoxide and a water soluble polymer are added in the    solvent, followed by stirring.

In this step, the metal alkoxide is hydrolyzed. On the surface of eachsoft magnetic material particle forming the Fe-based soft magneticmaterial powder, an insulating film containing a metal oxide, which is ahydrolysate of the metal alkoxide, and the water soluble polymer isformed.

By the procedure described above, a soft magnetic material powderincluding insulation-treated soft magnetic material particles can beobtained.

Hereinafter, a method for manufacturing this soft magnetic materialpowder will be described.

Fe-Based Soft Magnetic Material

The Fe-based soft magnetic material is the same as described above, andthe description thereof is omitted.

Solvent

As the solvent, an alcohol, such as methanol or ethanol, may be used.

Metal Alkoxide

As a metal element M of a metal alkoxide in the form of M-OR to beadded, at least one type selected from the group consisting of Li, Na,Mg, Al, Si, K, Ca, Ti, Cu, Sr, Y, Zr, Ba, Ce, Ta, and Bi may be used. Inaddition, for example, in consideration of the strength and the inherentspecific resistance of an oxide to be obtained, Si, Ti, Al, and Zr arepreferable.

In addition, as the alkoxy group OR of the metal alkoxide, an arbitrarygroup, such as a methoxy group, an ethoxy group, or a propoxy group, maybe selected.

In addition, at least two types of metal alkoxides may be used incombination.

In order to increase a hydrolysis rate of the metal alkoxide, if needed,there may be added an acidic catalyst, such as hydrochloric acid, aceticacid, or phosphoric acid; a basic catalyst, such as ammonia, sodiumhydroxide, or piperidine; or a salt catalyst, such as ammonium carbonateor ammonium acetate.

A dispersion liquid obtained after stirring may be dried by anappropriate method (oven, spray, in vacuo, or the like). A dryingtemperature may be, for example, in a temperature range of 50° C. to300° C. A drying time may be appropriately determined. For example, thedrying time may be, for example, in a range of 10 minutes to 24 hours.

Powder Magnetic Core

FIG. 2 is an enlarged cross-sectional view showing the structure of amagnetic core (powder magnetic core) 20 according to Embodiment 1. Thispowder magnetic core 20 is formed to have the structure in whichinsulating films 2 and a binder 12 surround the peripheries of Fe-basedsoft magnetic materials 1 derived from the cores of the soft magneticmaterial particles forming the soft magnetic material powder. Thisinsulating film 2 contains the inorganic oxide and the water solublepolymer, each of which is contained in the insulating film 2 of the softmagnetic material particle 10 included in the soft magnetic materialpowder. The binder 12 is formed of a binder which is added when a powdermagnetic core is manufactured.

In addition, in some cases, depending on the temperature of a heatannealing treatment, some of the functional groups of the water solublepolymer may be lost from the insulating film 2, or the water solublepolymer may be partially or entirely lost by heat decomposition,evaporation, or volatilization thereof.

Since this powder magnetic core 20 is formed using a soft magneticmaterial powder including the soft magnetic material particles eachhaving the thin insulating film 2, the soft magnetic materials 1 areisolated from each other with the insulating films 2 and the binder 12provided therebetween. Hence, without generating cracks in theinsulating film 2 of the soft magnetic material particle, a highelectric resistance can be maintained by the insulating film 2 and thebinder 12. As a result, the effect of low eddy-current loss can beobtained. In addition, since the insulating film 2 of the soft magneticmaterial particle 10 included in the soft magnetic material powder isthin, in the powder magnetic core 20, the thickness of the insulatingfilm 2 can also be decreased. As a result, the density of the softmagnetic material 1 can be increased, and a high magnetic permeabilitycan be obtained.

In addition, this magnetic core may also be used for a coil component oran electronic component, such as an inductor. In this case, in the coilcomponent, as the magnetic core, a member around which a coil-shapedconductor is wound may be mentioned. Alternatively, in the coilcomponent, as the magnetic core, a member in which a coil-shapedconductor is arranged may be mentioned. The coil-shaped conductor may bea wire wound in a coil form or a patterned conductor formed to have acoil shape may be mentioned.

Hereinafter, members forming this powder magnetic core will bedescribed.

Soft Magnetic Material

The soft magnetic material 1 is substantially the same as that of theabove Fe-based soft magnetic material, and the description thereof isomitted.

Insulating Film

The insulating film 2 is derived from the insulating film 2 of the softmagnetic material particle 10 included in the soft magnetic materialpowder. That is, the insulating film 2 contains an inorganic oxide and awater soluble polymer. However, the insulating film 2 of the magneticcore (hereinafter, referred to as “annealed magnetic core” in somecases) formed by heat annealing may contain no water soluble polymer insome cases. In addition, the inorganic oxide contained in the insulatingfilm 2 of the annealed magnetic core may include, besides the oxide ofthe above metal element M, an oxide of Fe in some cases. In addition, aninorganic oxide contained in the insulating film 2 of an annealedmagnetic core which uses an alloy (such as FeSiCr, FeSiBCr, or FeSiAl)containing Fe and Cr or Al as a soft magnetic material may furtherinclude, besides the oxide of the metal element M and the oxide of Fe,an oxide of Cr or an oxide of Al in some cases.

BinderThe binder 12 is a binder which is added when a powder magneticcore is manufactured. The binder 12 is not particularly limited as longas a thermosetting resin is used, and for example, an epoxy resin, animide resin, a silicone resin, or a fluorinated resin may be used. Thoseresins may be used alone, or at least two types thereof may beselectively used in combination. By the insulating film 2 and the binder12 described above, the soft magnetic materials 1 are isolated from eachother.

Method for Manufacturing Powder Magnetic Core

Next, a method for manufacturing a powder magnetic core will bedescribed.

-   (1) After the insulation-treated soft magnetic material powder thus    obtained is washed with ethanol and is then mixed with a    thermosetting resin functioning as the binder, compression molding    is performed, and subsequently, the thermosetting resin is cured by    heating. The temperature of the heat curing may be 10° C. to less    than 400° C. In addition, after the soft magnetic material powder    and the binder are mixed together, granulation may be performed.    Although the thermosetting resin used as the binder is not    particularly limited, for example, there may be mentioned an epoxy    resin, an imide resin, a silicone resin, or a fluorinated resin. One    type of those resins or a combination between at least two types    thereof may be selected. A curing agent curing the thermosetting    resin is not particularly limited, and for example, a phenol resin,    a polyamine, or an imidazole may be used. The binder may be added in    a range of 1 to 6 percent by weight with respect to 100 percent by    weight of the powder magnetic core. In addition, in order to    increase the strength of the powder magnetic core, a glass frit or a    silane coupling agent may also be used. Furthermore, in compression    molding, a die may also be used. By performing the compression    molding, the density of the soft magnetic material can be increased.    In addition, the compression molding is not essential and may be    performed if needed. A magnetic core obtained by performing the    compression molding is called a powder magnetic core. On the other    hand, a magnetic core obtained without performing the compression    molding is simply called a magnetic core. In this embodiment, the    “magnetic core” widely includes all types of magnetic cores    regardless of whether the compression molding is performed or not.-   (2) As for the powder magnetic core, in order to decrease the    magnetic core loss, a heat annealing treatment may be performed on a    heat-cured powder magnetic core. Since the magnetic core loss    depends on the frequency, the annealing treatment may be omitted in    accordance with a frequency band to be used for the powder magnetic    core. The annealing treatment may be performed on the powder    magnetic core at a temperature of 400° C. or more, if needed. In    particular, as for the annealing treatment, a heat treatment may be    performed, for example, in a temperature range of 400° C. to 900° C.    or furthermore in a temperature range of 600° C. to 900° C. in the    air, a N₂ atmosphere, or a N₂+H₂ atmosphere. As the binder used when    the heat annealing treatment is performed, a silicone resin is    preferable.

As described above, the magnetic core can be obtained. A magnetic coreobtained by performing an annealing treatment at 400° C. or more iscalled, for example, an annealed magnetic core. On the other hand, amagnetic core which is not processed by an annealing treatment iscalled, for example, a heat-cured magnetic core.

According to this method for manufacturing a powder magnetic core, asdescribed above, there is used a soft magnetic material powdercomprising the soft magnetic material particles each including the core1 which contains an Fe-based soft magnetic material and the insulatingfilm 2 which covers the surface of the core 1 and which contains aninorganic oxide and a water soluble polymer. Since a flexible watersoluble polymer is present in the insulating film 2 of the soft magneticmaterial particle 10, the stress generated in compression molding can bereduced, and hence, molding can be performed at a low pressure. As aresult, even in powder compaction molding for manufacturing a powdermagnetic core, cracks are not generated in the insulating film 2 of thesoft magnetic material particle 10 included in the soft magneticmaterial powder, and the insulating film 2 and the binder 12 are notbroken. As a result, in this powder magnetic core, a high electricresistance can be realized, and the effect of low eddy-current loss canbe obtained.

Hereinafter, with reference to Tables 1 and 2, Examples 1 to 19 andComparative Examples 1 to 3 will be described.

Manufacturing conditions of soft magnetic material powders and powdermagnetic cores are shown in Table 1, and the measurement values and theevaluation results are shown in Table 2.

TABLE 1 Inorganic Oxide Water Soluble Polymer Blending Blending MoldingAnnealing Magnetic Amount Amount Pressure Warm Treatment Material RawMaterial Product (wt %) Name (wt %) (t/cm²) Molding (° C.) Example 1FeSiCr Tetraethyl SiO₂ 1 Poly(vinyl 0.1 4 No 720 Orthosilicatepyrrolidone) Example 2 FeSiCr Tetraethyl SiO₂ 0.01 Poly(vinyl 0.1 4 No720 Orthosilicate pyrrolidone) Example 3 FeSiCr Tetraethyl SiO₂ 5Poly(vinyl 0.1 4 No 720 Orthosilicate pyrrolidone) Example 4 FeSiCrTetraethyl SiO₂ 1 Poly(vinyl 0.01 4 No 720 Orthosilicate pyrrolidone)Example 5 FeSiCr Tetraethyl SiO₂ 1 Poly(vinyl 1 4 No 720 Orthosilicatepyrrolidone) Example 6 FeSiCr Tetraethyl SiO₂ 1 Poly(ethylene 0.1 4 No720 Orthosilicate imine) Example 7 FeSiCr Tetraethyl SiO₂ 1Carboxymethyl 0.1 4 No 720 Orthosilicate Cellulose Example 8 FeSiCrTetraethyl SiO₂ 1 Gelatin 0.1 4 No 720 Orthosilicate Example 9 FeSiCrTetraethyl SiO₂ 1 Poly(acrylic 0.1 4 No 720 Orthosilicate acid) Example10 FeSiCr Tetraethyl SiO₂ 1 Poly(ethylene 0.1 4 No 720 Orthosilicateglycol) Example 11 FeSiCr Tetraethyl SiO₂ 1 Poly(vinyl 0.1 4 No 720Orthosilicate alcohol) Example 12 FeSiCr Aluminum Al₂O₃ 1 Poly(vinyl 0.14 No 720 lsopropoxide pyrrolidone) Example 13 FeSiCr Titanium TiO₂ 1Poly(vinyl 0.1 4 No 720 Tetraisopropoxide pyrrolidone) Example 14 FeSiCrZirconium-n- ZrO 1 Poly(vinyl 0.1 4 No 720 Butoxide pyrrolidone) Example15 FeSiCr Tetraethyl SiO₂ 1 Poly(vinyl 0.1 4 No No Orthosilicatepyrrolidone) Example 16 FeSiCr Tetraethyl SiO₂ 0.01 Poly(vinyl 0.1 4 NoNo Orthosilicate pyrrolidone) Example 17 FeSiCr Tetraethyl SiO₂ 5Poly(vinyl 0.1 4 No No Orthosilicate pyrrolidone) Example 18 FeSiCrTetraethyl SiO₂ 1 Poly(vinyl 0.01 4 No No Orthosilicate pyrrolidone)Example 19 FeSiCr Tetraethyl SiO₂ 1 Poly(vinyl 1 4 No No Orthosilicatepyrrolidone) Comparative FeSiCr — — 0 — 0 8 Yes 720 Example 1Comparative FeSiCr Tetraethyl SiO₂ 1 — 0 4 No 720 Example 2Orthosilicate

TABLE 2 1 MHz Specific Magnetic Specific Resistance Permeability (Ω ·cm) Evaluation Example 1 39 6.0 × 10¹¹ ∘ Example 2 39 1.0 × 10¹¹ ∘Example 3 39 3.5 × 10¹¹ ∘ Example 4 37 1.8 × 10¹¹ ∘ Example 5 33 4.3 ×10¹¹ ∘ Example 6 35 3.9 × 10¹¹ ∘ Example 7 36 4.5 × 10¹¹ ∘ Example 8 383.4 × 10¹¹ ∘ Example 9 36 5.4 × 10¹¹ ∘ Example 10 35 3.0 × 10¹¹ ∘Example 11 37 3.4 × 10¹¹ ∘ Example 12 37 6.4 × 10¹¹ ∘ Example 13 38 4.2× 10¹¹ ∘ Example 14 36 7.4 × 10¹¹ ∘ Example 15 30 6.0 × 10¹³ ∘ Example16 31 5.0 × 10¹³ ∘ Example 17 30 4.8 × 10¹³ ∘ Example 18 31 1.9 × 10¹³ ∘Example 19 30 3.8 × 10¹³ ∘ Comparative 39 1.5 × 10⁵  x Example 1Comparative 20 4.2 × 10⁷  x Example 2

EXAMPLE 1 Insulating Treatment of Soft Magnetic Material Powder

A method for manufacturing a soft magnetic material powder according toExample 1 will be described.

-   (a) In 37.2 g of ethanol, 20 g of a FeSiCr powder having an average    particle diameter of 30 μm was added as a soft magnetic material.-   (b) Next, 1 percent by weight of tetraethyl orthosilicate was    weighed on a SiO₂ basis with respect to 100 percent by weight of the    Fe-based soft magnetic material and was then added to and stirred    with the ethanol to which the FeSiCr powder was added.-   (c) Furthermore, a poly(vinyl pyrrolidone) was weighed so as to have    a concentration of 0.1 percent by weight with respect to 100 percent    by weight of the Fe-based soft magnetic material, was dissolved in    3.2 g of purified water, and was then dripped to the ethanol to    which the FeSiCr powder was added. Stirring and mixing were    performed over 60 minutes.

Accordingly, an insulation-treated soft magnetic material powder (onwhich an insulating film was formed) was obtained.

Formation and Quality Confirmation of Powder Magnetic Core Using SoftMagnetic Material Powder

Next, the formation of a powder magnetic core using theinsulation-treated soft magnetic material powder thus obtained will bedescribed.

-   (1) After 500 g of the insulation-treated soft magnetic material    powder thus obtained and 20.9 g of a silicone resin functioning as a    binder were mixed together, toroidal rings each having an inside    diameter of 4 mm, an outside diameter of 9 mm, and a thickness of 1    mm were formed at a pressure of 4 t/cm². In addition, at a pressure    of 4 t/cm², test pieces each having a size of 3 mm×3 mm×1 mm were    formed.-   (2) Next, the toroidal rings and the test pieces were heated at    200° C. for 1 hour (curing treatment).-   (3) Furthermore, some toroidal rings and test pieces were heated at    720° C. for 50 minutes in an air atmosphere (heat annealing    treatment).-   (4) Subsequently, the magnetic permeability of the toroidal ring was    measured at 1 MHz using a RF impedance analyzer (Agilent E4991A). In    addition, by a high resistance measurement device (Advantest R8340A    ULTRA HIGH RESISTANCE METER), a voltage of 900 V was applied for 5    seconds between two points of the test piece having a gap of 3 mm,    and the specific resistance was measured.

When the specific magnetic permeability obtained from the measuredmagnetic permeability was 30 or more, and when the specific resistancewas 10⁸ Ω·cm or more, the evaluation result was represented by O(accepted), and when at least one of them was less than the valuedescribed above, the evaluation result was represented by X (rejected).

FIG. 3 is a schematic view showing analytical positions at each of whicha composition analysis is performed, the analytical positions beinglocated on the line extending from the core to the insulating film andthe binder of the soft magnetic material particle which forms thecross-sectional structure of the magnetic core shown in FIG. 2. FIG. 4is a graph showing the composition analysis results obtained along theline shown in FIG. 3. The composition analysis of the cross-sectionalstructure of the magnetic core was performed as described below. First,a surface of the test piece processed by a heat annealing treatment, thesurface being perpendicular to a side of the test piece having thesmallest length, was polished until the length of the side having thesmallest length is decreased to one-half, so that the cross-sectionalsurface was formed. Subsequently, line analysis of the cross-sectionalsurface was performed by TEM-EDS on each of the analytical positions onthe line shown in FIG. 3, so that the elements present in the core 1,the insulating film 2, and the binder 12 on the line were analyzed.

Withstand Voltage Test

FIG. 5 is a graph showing the relationship between the specificresistance measured by the above high resistance measurement device andthe applied voltage. In Examples 1 and 2, even when a voltage of 900 Vwas applied, IR (insulating resistance) was not decreased. On the otherhand, in Comparative Example 1, when a voltage of 900 V was applied, IR(insulating resistance) was decreased.

From this test, it was found that in Examples 1 and 2 according to thepresent disclosure, a magnetic core having a high withstand voltagecapable of withstanding an application voltage of 900 V could beprovided.

Operation and Effect

As shown in Table 2, from the soft magnetic material powder according toExample 1, the powder magnetic core could be formed at a low moldingpressure (4 t/cm²). The powder magnetic core thus obtained had a highspecific magnetic permeability (39), and even after the heat annealingtreatment was performed, the specific resistance was high (6.0×10¹¹Ω·cm). In addition, from the results obtained from the line analysisshown in FIG. 4, in the soft magnetic material powder according toExample 1, the amount of Si in the obtained insulating film 2 was largerthan that of Cr therein. The soft magnetic material powder according toExample 1 includes the core 1 which is formed from an Fe-based softmagnetic material and which contains Cr and the insulating film 2 whichcovers the surface of the core 1 and which contains Si. Furthermore, inthe insulating film 2, an inorganic oxide in which the amount of Si islarger than that of Cr is contained.

From this analysis result, in comparison between Example 1 andComparative Example 1, it is believed that since a large amount of Si iscontained in the insulating film 2 as compared to that of Cr, a magneticcore having a high withstand voltage can be obtained.

EXAMPLES 2 and 3

Except that as shown in Table 1, the addition amount of the tetraethylorthosilicate used as the metal alkoxide was changed (Example 2: 0.01percent by weight, Example 3: 5 percent by weight), a soft magneticmaterial powder and a powder magnetic core were formed in a mannersimilar to that of Example 1, and the measurement and the evaluationwere performed.

Operation and Effect

As shown in Table 2, as was the case of Example 1, the powder magneticcore could be formed at a low molding pressure (4 t/cm²). In addition,the powder magnetic core thus obtained had a high specific magneticpermeability (Example 2: 39, Example 3: 39), and even after the heatannealing treatment was performed, the specific resistance was high(Example 2: 1.0×10¹¹ Ω·cm, Example 3: 3.5×10¹¹ Ω·cm).

EXAMPLES 4 and 5

Except that as shown in Table 1, the addition amount of the poly(vinylpyrrolidone) used as the water soluble polymer was changed (Example 4:0.01 percent by weight, Example 5: 1 percent by weight), a soft magneticmaterial powder and a powder magnetic core were formed in a mannersimilar to that of Example 1, and the measurement and the evaluationwere performed.

Operation and Effect

As shown in Table 2, as was the case of Example 1, the powder magneticcore could be formed at a low molding pressure (4 t/cm²). In addition,the powder magnetic core thus obtained had a high specific magneticpermeability (Example 4: 37, Example 5: 33), and even after the heatannealing treatment was performed, the specific resistance was high(Example 4: 1.8×10¹¹ Ω·cm, Example 5: 4.3×10¹¹ Ω·cm).

EXAMPLES 6 to 11

Except that as shown in Table 1, the type of water soluble polymer to beused was changed (Example 6: poly(ethylene imine), Example 7:carboxymethyl cellulose, Example 8: gelatin, Example 9: poly (acrylicacid), Example 10: poly(ethylene glycol), Example 11: poly(vinylalcohol)), a soft magnetic material powder and a powder magnetic corewere formed in a manner similar to that of Example 1, and themeasurement and the evaluation were performed.

Operation and Effect

As shown in Table 2, as was the case of Example 1, the powder magneticcore could be formed at a low molding pressure (4 t/cm²). In addition,the powder magnetic core thus obtained had a high specific magneticpermeability (Example 6: 35, Example 7: 36, Example 8: 38, Example 9:36, Example 10: 35, Example 11: 37), and even after the heat annealingtreatment was performed, the specific resistance was high (Example 6:3.9×10¹¹ Ω·cm, Example 7: 4.5×10¹¹ Ω·cm, Example 8: 3.4×10¹¹ acm,Example 9: 5.4×10¹¹ Ω·cm, Example 10: 3.0×10¹¹ Ω·cm, Example 11:3.4×10¹¹ Ω·cm).

EXAMPLES 12 to 14

Except that as shown in Table 1, the type of metal alkoxide to be usedwas changed (Example 12: aluminum isopropoxide, Example 13: titaniumtetraisopropoxide, Example 14: zirconium-n-butoxide), a soft magneticmaterial powder and a powder magnetic core were formed in a mannersimilar to that of Example 1, and the measurement and the evaluationwere performed.

Operation and Effect

As shown in Table 2, as was the case of Example 1, the powder magneticcore could be formed at a low molding pressure (4 t/cm²). In addition,the powder magnetic core thus obtained had a high specific magneticpermeability (Example 12: 37, Example 13: 38, Example 14: 36), and evenafter the heat annealing treatment was performed, the specificresistance was high (Example 12: 6.4×10¹¹ Ω·cm, Example 13: 4.2×10¹¹acm, Example 14: 7.4×10¹¹ Ω·cm).

EXAMPLE 15

Except that as shown in Table 1, the heat annealing treatment was notperformed, a soft magnetic material powder and a powder magnetic corewere formed in a manner similar to that of Example 1, and themeasurement and the evaluation were performed.

Operation and Effect

As shown in Table 2, according to the powder magnetic core of Example15, the formation thereof could be formed at a low molding pressure, andalthough the heat annealing treatment was not performed, a high specificmagnetic permeability (30) and a high specific resistance (6.0×10¹³Ω·cm) could be obtained.

EXAMPLES 16 and 17

Except that as shown in Table 1, the addition amount of the tetraethylorthosilicate used as the metal alkoxide was changed (Example 16: 0.01percent by weight, Example 17: 5 percent by weight), a soft magneticmaterial powder and a powder magnetic core were formed in a mannersimilar to that of Example 15, and the measurement and the evaluationwere performed.

Operation and Effect

As shown in Table 2, as was the case of Example 15, the powder magneticcore could be formed at a low molding pressure, and although the heatannealing treatment was not performed, a high specific magneticpermeability (Example 16: 31, Example 17: 30) and a high specificresistance (Example 16: 5.0×10¹³ Ω·cm, Example 17: 4.8×10¹³ Ω·cm) couldbe obtained.

EXAMPLES 18 and 19

Except that as shown in Table 1, the addition amount of the poly(vinylpyrrolidone) used as the water soluble polymer was changed (Example 18:0.01 percent by weight, Example 19: 1 percent by weight), a softmagnetic material powder and a powder magnetic core were formed in amanner similar to that of Example 15, and the measurement and theevaluation were performed.

Operation and Effect

As shown in Table 2, as was the case of Example 15, the powder magneticcore could be formed at a low molding pressure, and although the heatannealing treatment was not performed, a high specific magneticpermeability (Example 18: 31, Example 19: 30) and a high specificresistance (Example 18: 1.9×10¹³ Ω·cm, Example 19: 3.8×10¹³ Ω·cm) couldbe obtained.

Comparative Examples 1 and 2

As shown in Table 1, in Comparative Example 1, by the use of a magneticpowder which was not processed by an insulating treatment, granulationwas formed in a manner similar to that of Example 1, and a powdermagnetic core was then formed at a molding pressure of 8 t/cm² whileheating was performed at 150° C.

In Comparative Example 2, except that the poly(vinyl pyrrolidone)functioning as the water soluble polymer was not added, a soft magneticmaterial powder and a powder magnetic core were formed in a mannersimilar to that of Example 1.

Operation and Effect

As shown in Tables 1 and 2, according to Comparative Example 1, althougha powder magnetic core having a high specific magnetic permeability (39)could be obtained, a high molding pressure (8 t/cm²) and warm moldingwere required, and since the insulating treatment of the soft magneticmaterial powder was not performed, the specific resistance after theheat annealing treatment was decreased (1.5×10⁵ Ω·cm).

In Comparative Example 2, a powder magnetic core having a relatively lowspecific magnetic permeability (20) was only obtained. In addition, inthe pressure molding, fine cracks were generated in the insulating film,and the specific resistance was decreased (4.2×10⁷ Ω·cm).

In addition, in the above examples, although FeSiCr was used as themagnetic material, the magnetic material is not limited thereto, andanother Fe-based soft magnetic material may also be used. In addition,the temperature of the heat annealing treatment is not limited to 720°C., and the heat annealing treatment may be performed when thetemperature is set in a range of 400° C. to 900° C. and furthermore in arange of 600° C. to 900° C.

In addition, in the present disclosure, the various embodimentsdescribed above may be arbitrarily used in combination, and theadvantages of the individual embodiments may also be obtained.

INDUSTRIAL APPLICABILITY

According to the soft magnetic material powder of the presentdisclosure, as the soft magnetic material, a sufficient density and ahigh magnetic permeability can be obtained, and furthermore, a magneticcore having a high electric resistance and a high withstand voltage canalso be obtained by the insulating films and the binder of the softmagnetic material particles included in the soft magnetic materialpowder, and hence, the above soft magnetic material powder iseffectively used as a soft magnetic material powder for magnetic cores.

1. A soft magnetic material powder comprising: soft magnetic materialparticles, wherein the soft magnetic material particles each include: acore containing an Fe-based soft magnetic material; and an insulatingfilm covering the surface of the core, and the insulating film containsan inorganic oxide and a water soluble polymer.
 2. The soft magneticmaterial powder according to claim 1, wherein the water soluble polymeris at least one selected from the group consisting of a poly(vinylpyrrolidone), a poly(ethylene imine), a carboxymethyl cellulose, agelatin, a poly (acrylic acid), a poly(ethylene glycol), and apoly(vinyl alcohol).
 3. The soft magnetic material powder according toclaim 1, wherein the water soluble polymer is a poly(vinyl pyrrolidone)and is contained in a range of 0.01 to 1 percent by weight with respectto 100 percent by weight of the Fe-based soft magnetic material.
 4. Thesoft magnetic material powder according to claim 1, wherein theinorganic oxide is at least one selected from the group consisting ofTiO₂, SiO₂, Al₂O₃, and ZrO.
 5. The soft magnetic material powderaccording to claim 1, wherein the inorganic oxide is SiO₂ and iscontained in a range of 0.01 to 5 percent by weight with respect to 100percent by weight of the Fe-based soft magnetic material.
 6. The softmagnetic material powder according to claim 1, wherein the Fe-based softmagnetic material is at least one selected from the group consisting ofFe, FeNi, FeCo, FeSi, FeSiCr, FeSiAl, and FeSiBCr.
 7. A method formanufacturing a soft magnetic material powder, the method comprising:dispersing an Fe-based soft magnetic material in a solvent; and adding ametal alkoxide, a water soluble polymer, and water to the solventfollowed by stirring to form insulating films each containing a metaloxide, which is a hydrolysate of the metal alkoxide, and the watersoluble polymer on surfaces of soft magnetic material particles whichform the Fe-based soft magnetic material powder, so that an insulatingtreatment is performed on the soft magnetic material particles.
 8. Amagnetic core comprising the soft magnetic material powder according toclaim
 1. 9. A magnetic core comprising: soft magnetic materialparticles; and a binder which bonds the soft magnetic material particlesto each other, wherein the soft magnetic material particles eachinclude: a core containing an Fe-based soft magnetic material; and aninsulating film covering the surface of the core, the insulating filmcontains an inorganic oxide and a water soluble polymer.
 10. A magneticcore comprising: soft magnetic material particles; and a binder whichbonds the soft magnetic material particles to each other, wherein thesoft magnetic material particles each include: a core formed from anFe-based soft magnetic material; and a Si-containing insulating filmcovering the surface of the core, the Fe-based soft magnetic materialincludes Fe and Cr, and the insulating film contains an inorganic oxidein which the amount of Si is larger than that of Cr.
 11. A method formanufacturing a magnetic core, the method comprising: mixing the softmagnetic material powder according to claim 1 and a thermosetting resinfunctioning as a binder to form a mixture; and heat-curing thethermosetting resin of the mixture to obtain a magnetic core.
 12. Amethod for manufacturing a magnetic core, the method comprising: mixingthe soft magnetic material powder according to claim 1 and athermosetting resin functioning as a binder to form a mixture; and afterthe thermosetting resin is cured by heating the mixture, performing anannealing treatment to obtain a magnetic core.
 13. An electroniccomponent comprising the magnetic core according to claim 8.